The role of torque in haptic perception of object location in virtual environments

An experimental study was performed with human subjects to determine the role of torque feedback in purely haptic perception of object location within virtual environments. The experimental hardware consisted of two Phantom haptic interface devices connected by a common stylus. Ray-based rendering technique that models the user-controlled stylus as a line was used for computing collision detection with a virtual object and its force as well as torque response. The subjects were trained with correct-answer feedback to obtain their best performance. Results demonstrate that the most significant improvement in perception occurred during the first training session. They also show that identification of object location by purely haptic cues through a tool can be accomplished in two distinct ways: (1) with full force and torque feedback, even when only tapping with a fixed orientation of the stylus is permitted; and (2) with only force at the stylus tip reflected back to the user, when multiple stylus orientations ('rocking') are allowed in contacting the object. Under these conditions, the estimated JND, which is expected to be an upper bound, ranged from about 22% for the nearest locations to 12% for the farthest locations.